An out-of-control car blasted into an auto-body shop in Queens today, killing one mechanic and chopping off the legs of another, authorities said.

Witnesses wrapped tourniquets around the 30-year-old legless victim’s thighs — he’s in serious condition at New York Hospital in Queens, officials said.

The mayhem began when a boxing trainer from Astoria, Jim Hart, was driving his 1998 black Mercedes Benz across the street from Citi Field when a blue 1992 Toyota Corolla hit his rear bumper, then veered into the 126th Street shop around 11:40 am.

“It was bizarre because there were no other cars on the street,” Hart, 43, told The Post. “I kept wondering why he was hitting me. I figured maybe he was trying to rob me. He must have lost it.”

Hart tied a yellow rope around the legless victim to contain the bleeding, he said.

The Toyota also rammed in to a 33-year-old mechanic, throwing him to the back of the shop and killing him, officials said.

“Everyone stopped, the whole street,” Hart said. “There was no noise. No screaming. No nothing. All the mechanics just ran out and stopped and stared. I ran over and tied rope on the guy’s legs.”

The Toyota driver got out of his car with a cane and stood expressionless in a pool of blood.

One worker at the auto body shop said the Toyota was speeding.

Safiullah Mir, 49, of the New Pamir Auto-body shop said it seemed like the Toyota was going 100 mph. He cried when recounting the horrific death of an employee.

“He died instantly,” he said. “He was very educated, very sociable,a sweet, sweet man.”

The driver was taken away in an ambulance. Police did not release the names because family hadn’t been notified and no one has been charged..